Color television display tube with ferromagnetic screening member



Jan. 14, 1969 R R BATHELT ET AL 3,422,220

COLOR TELEVISION DISPLAY TUBE WITH FERROMAGNETIC SCREENING MEMBER Filed May 10, 1966 INVENTORS ROBERT RigTHELT CONSTANT J.W. PANIS BY GENT United States Patent Delaware Filed May 10, 1966, Ser. No. 549,036 Claims priority, application Netherlands, June 9, 1965,

6507304 US. Cl. 178-732 8 Claims Int. Cl. H01j 29/02 The invention relates to a color television display tube provided with a ferromagnetic screening hood which covers the major part of the cone. Moreover, the cone and the window are provided with ground edges, which are connected with each other by means of a readily melting kind of glass (glaze), while the side face of the window is provided with smoothly ground glass reference lugs. In particular, the invention relates to such a display tube in which the screening hood serves, in addition, to prevent implosion. v

In monochrome display tubes an annular band is placed around the outer side of the window and the space between this band and the glass filled with a suitable material. Although the annular band does not exert a pressure on the bulb of the tube, cracks in the glass are prevented from continuing beneath the band, so that implosion is avoided.

With such monochrome display tubes it is immaterial whether the annular band is broad or narrow or whether the sealing edges of the cone and the window are covered or are not covered by the filling material.

Since, in general, the annular band holds, at the same time, the members for fastening the tube in the cabinet of the apparatus, the width of the annular band is usually chosen in accordance with the desired place of said fastening members.

In color television display tubes the edges of the cone and the window to be connected with each other are, however, not sealed, but they are interconnected by means of a glaze, since the phosphor screen and the color selection electrodes would otherwise become too hot and oxidation and deformation might occur. Moreover, the side face of the upright edge of'the cup-shaped window is provided with glass reference lugs, which are ground smooth until they have the correct height. These lugs serve for fixing the window accurately in a given position during the manufacture of the phosphor screen.

It has been found that such a ground glass part must not be covered by the filling material of an anti-implosion annular band. During the grinding process the ground surfaces have sharp side edges, which may be readily damaged. Moreover, owing to the grinding process, fine hairline cracks are produced in the glass surface. Since the glass itself is not melted when the glass edges of the window and the cone are interconnected by means of glaze, these damage and hairline cracks are left in the junction, so that it is not permissible to expose this seam, in addition to the expansion and shrinkage forces of the filling material due to temperature fluctuations, since these cracks may be prolonged and may give rise to leakage. 11he same applies to the ground surface of the reference ugs.

Thus, an annular band for a monochrome display tube having a width such that it covers the junction must therefore not be applied to a color television display tube without taking further steps to avoid those difficulties. A broad annular band is, however, highly desirable for a color display tube, since such a display tube is comparatively heavy due to the provision of the color selection elec- 3,422,220 Patented Jan. 14, 1969 trodes, which are usually fastened to a rigid metal frame. In order not to expose the screening hood to heavy bendin=g forces, it is therefore desirable for the fastening members of the tube connected with the hood to be arranged approximately near, or in a plane going through the center of gravity of the tube. This center of gravity is located approximately at the level of the juncture between the cone and the window. Therefore, the fastening members will also be arranged in or near the plane of the seam.

A suitable embodiment of such a display tube is obtained, in accordance with the invention, by buildin up the ferromagnetic screening hood from two inter-engaging, annular portions. One portion surrounding the Window holds the members for fastening the tube in the cabinet, the width of that portion being such that it extends beyond the juncture between the cone and the window. The space between this annular portion and the side face of the window is filled round about at least partly with a suitable hardenable filling material, so that this annular portion operates as an anti-implosion band. Furthermore, steps are taken for keeping the juncture between the cone and the window and the ground faces of the reference lugs clear of adhesive contact with said filling material. The reference lugs :are preferably covered with adhesive tape, while the seam between the window and the cone may also be covered with adhesive tape. It is furthermore possible to apply a liquid layer, for example oil, to said faces, or a suitable paint.

The space between the :annular portion adjacent the display face and the bulb is preferably filled up to about 5 mms. from the juncture, since this requires a smaller quantity of filling material, while the juncture need not be covered with adhesive tape.

It is desirable for the two portions of the screening hood to be electrically insulated from each other, since the portion surrounding the cone is connected with the conducting layer applied to the cone, which layer, in turn, is in contact with the chassis. The chassis is, in general, connected with one terminal of an electrical power supply, so that it may be at a potential with respect to ground.

It has been found that the embodiment according to the invention provides a suitable combination of an antiimplosion ring band and the magnetic screening hood.

Although the space between the cone and the associated portion of the screening hood also may be filled with a filling material, this is of no practical use. This portion of the screening hood can best be caused to bear on the cone wall by means of ridges or spacers.

The invention will be described more fully with reference to the drawing, in which FIG. 1 is a partial sectional view and FIG. 2 is a side elevation of a color television display tube according to the invention.

Referring to the drawing, a color television tube includes a glass window and a glass cone 2, the edges 4 and 5 of which are joined by a glaze 3, after these edges 4 and 5 have been ground flat. Thus sharp side edges are formed, which may be readily damaged and may exhibit hairline cracks.

A metal frame 6 is arranged inside the bulb on which a color selection electrode 7, e.g., a shadow mask, is secured. A phosphor screen 8 consisting of a great number of dots or phosphors luminescing in the colors red, green and blue is applied to the inner side of the display surface of window 1.

Window 1 and cone 2 are surrounded by a ferromagnetic screening hood consisting of an annular portion 9, which surrounds the display area, and an annular portion 10, which partly surrounds the cone and extends up to a few centimeters from the foremost deflection coil. Portion 10 is joined to portion 9 by a ring 11, for example of a synthetic resin, having an H-shaped cross section, but is "ice insulated electrically from the latter portion. Portion 10 is furthermore connected electrically by means of one or more contact springs 12 to the conducting layer 13 on the cone and bears on the cone by means of depressed portions 16. On the side face of window 1 eight ground glass reference lugs 17 are provided.

Annular portion 9 extends beyond juncture 3 and is provided with welded ears 14, which serve for fastening the display tube in a cabinet. Bars 14 are located in a plane which passes approximately through the center of gravity of the tube, so that no bending forces are exerted on the annular portion 9. The space between portion 9 and the side face of the window 1 is filled partly round about with a suitable hardenable material, preferably a synthetic resin or a mixture of substances. If desired, graphite or a metal powder may be added to the filling material, so that it is slightly conductive and the portion 9 is connected through a high-value resistance to the coating 13, so that electrostatic charges are conducted away from this portion. The reference lugs 17 were previously covered with a strip of adhesive tape or a layer of a suitable paint 18, to keep the ground surfaces clear of filling material 15. When use is made of a very hard filling material which does not adhere to glass, coating of the juncture presents no difficulties, since the surface of the glaze is smooth. However, the rough, ground faces of the lugs would nevertheless adhere too strongly to the filling material, so that these have to be covered.

Since the portion 10 of the screen is connected to the source of electric power an insulating path of at least 4 mms. across the surface of the insulating ring 11 between the portions 9 and 10 must be left.

It appears that in spite of the fact that the space between the portion 9 and the bulb is filled up only to about to mms. from the juncture, this portion can still operate as an anti-implosion band. The rim of portion 9 may be left clear of the filling material and is suffi-ciently rigid to support the tube by means of the ears 14 in a cabinet, since the center of gravity of the tube is located in or near the plane of the ears 14. The juncture, like the reference lugs, may be covered with adhesive tape or a suitable layer of paint or the like, while the filling material may extend in this case across the seam. The quantity of filling material is then considerably greater, while covering of the juncture is an elaborate process.

Owing to the rather large distance of ears 14 from the display surface, the window of the tube may be arranged so as to project from the cabinet at the front, which may be advantageous in some cases.

Although a single embodiment is described herein, other embodiments of the invention are possible. Bars 14, for example, may be connected to the portion 9 in the re verse sense or they may be integral therewith. The space around the seam of the window and the cone may be filled with a soft, elastic coating substance in order to prevent penetration of moisture, if a hard filling material which adheres poorly to glass is employed.

Therefore, while the invention has been described with reference to this single embodiment, other modifications will be apparent to those skilled in this art without departing from the spirit and scope of the invention which is defined in the appended claims.

What is claimed is:

1. A cathode-ray tube for color television display comprising an envelope having adjoining cone and window portions having smoothly ground edges joined by a glazelike material, said window portion having a side face provided with reference extensions, a ferromagnetic screening hood surrounding said side face of the window and a major portion of the cone, said hood further comprising two joined annular portions, one of which surrounds and is spaced from the side-face of the window and supports members for positioning the tube in a housing, said portion having a width such that said portion extends beyond the juncture between the cone and the window, and a filler material filling the space between said portion and the side-face of the window whereby said portion serves an anti-implosion member, said juncture between the cone and the window and the surfaces of said reference extensions being free of an adhesive contact with said filler material.

2. A color television display tube as claimed in claim 1, in which the ground surfaces of the reference extensions are separated from the filling material by an intermediate layer.

3. A color televison display tube as claimed in claim 2, in which the intermediate layer consists of an adhesive material.

4. A color television display tube as claimed in claim 1, in which the filling material remains at a distance of at least 5 mms. from the juncture of the window and the cone.

5. A color television display tube as claimed in claim 1, in which the juncture between the window and the cone is coated with a layer of a substance which prevents adhesion of the filling material at the juncture.

6. A color television display tube as claimed in claim 1, in which the ground surfaces of the reference extensions and the juncture between the window and the cone are covered with an intermediate layer of a liquid which prevents adhesion of the filling material thereto.

7. A color television display tube as claimed in claim 5, in which the liquid is an oil.

8. A color television display tube as claimed in claim 1, in which the center of gravity of the tube is located in proximity to a plane passing through the members for positioning the tube in the housing.

References Cited UNITED STATES PATENTS 3,278,682 10/1966 Panis et a1 l787.8 3,340,358 9/1967 De Gier et al. l787.82 3,369,074 2/1968 Massa. l787.82

ROBERT L. GRIFFIN, Primary Examiner.

R. K. ECKERT, JR., Assistant Examiner. 

1. A CATHODE-RAY TUBE FOR COLOR TELEVISION DISPLAY COMPRISING AN ENVELOPE HAVING ADJOINING CONE AND WINDOW PORTIONS HAVING SMOOTHLY GROUND EDGES JOINED BY A GLAZELIKE MATERIAL, SAID WINDOW PORTION HAVING A SIDE FACE PROVIDED WITH REFERENCE EXTENSIONS, A FERROMAGNETIC SCREENING HOOD SURROUNDING SAID SIDE FACE OF THE WINDOW AND A MAJOR PORTION OF THE CONE, SAID HOOD FURTHER COMPRISING TWO JOINED ANNULAR PORTIONS, ONE OF WHICH SURROUNDS AND IS SPACED FROM THE SIDE-FACE OF THE WINDOW AND SUPPORTS MEMBERS FOR POSITIONING THE TUBE IN A HOUSING, SAID PORTION HAVING A WIDTH SUCH THAT SAID PORTION EXTENDS BEYOND THE JUNCTURE BETWEEN THE CONE AND THE WINDOW, AND A FILLER MATERIAL FILLING THE SPACE BETWEEN SAID PORTION AND THE SIDE-FACE OF THE WINDOW WHEREBY SAID PORTION SERVES AN ANTI-IMPLOSION MEMBER, SAID JUNCTURE BETWEEN THE CONE AND THE WINDOW AND THE SURFACES OF SAID REFERENCE EXTENSIONS BEING FREE OF AN ADHESIVE CONTACT WITH SAID FILLER MATERIAL. 